help with math homework ! : (

[celine_dion_fan]

So I went to my teacher yesterday and all he gave me was the answers. No explenation or anything .

I have a test on tuesday and I want to know how to work the problem. Me and my group are really stressing out. We dont have

book for class only powerpoints and he hasn't even posted them yet. Im really stressing out ! I would really apreciate it any help.

 

Scores on a well known test of creativity are normally distributed in the population,

with a population mean of 450 and a population standard deviation of 96.

All scores on the test are whole numbers.

 

1. Calculate the percentile ranks for the following scores

400 -

2. Calculate the following percentiles.

45th -

3. What is the probability (to four decimal places) of randomly selecting someone who scored

greater than 516?

less than 616?

 

Thanks a bunch !!!

Edited September 27, 2008 at 04:30 AM by celine_dion_fan

[wolfepaw]

Sofie, isn't stats fun? No, huh. Here's a link you might want to read that might be helpful.

http://www.regentsprep.org/Regents/math/al...ormalLesson.htm

 

In the meantime, I am going to try to work this out myself. It's been awhile since I've had to do any stats, but I used to be pretty good at it.

 

Hope this helps.

[beautyroses]

it is a bit hard to describe I will type it in word and send it to your mail if yu give me your mail

for second question you should calculate the integrated of the distribution and put the higher limit (x) and this integrate should be equal to 0.45 the do the integrate it will goes to a qulibiruim

I hope I am helpful my english sucks when it goes to teaching math it will be easier if I write it in mathematic form.

[wolfepaw]

Did he give a value of N (number in the population)? Anyway, here is a picture of the normal curve with the corresponding values for this problem under it. You can make some estimates from the table itself for the first 2 question you have. I don't know if he wants you to give the exact answers, if so you may need to use a calculator (involves area under the curve). Anyway. here's what I came up with:

 

 

 

http://www.regentsprep.org/Regents/math/algtrig/ATS2/normal67.gif

Value 162 210 258 306 354 402 450 498 546 594 642 690 738

%tile 0.1th 0.6th 2.3rd 6.7th 15.9th 30.9th 50th 69.1th 84.1th 93.3th97.7th99.4th99.9th

 

The numbers on the X-axis represent the SDs (I calculated the values under that from the data you gave), the numbers in the histogram represent percentage of population falling along those numbers. This is based on a normal distribution and it may for continuous numbers as opposed to discreet (integers only), but I think it would still apply. I'm sorry the numbers don't line up when I previewed the message, but the numbers correspond to each of the SD numbers.

 

So using the chart, percentile rank for 400 would fall pretty close to the 30th percentile (just slightly below 402 on graph).

The 45th percentile would be between 402 and 450 (almost exactly), so it would be approximately 426.

 

The exact probability of selecting someone who scored greater than 516. Well, that's only about 0.69 of the SD, so it would be about 26% chance (percentage of pop above 516). The exact probability of selecting someone who scored less than 616 - that's about 1.7 SD so the would be about a 95% chance (percentage of pop below 616).

 

I know these aren't exact answers, but you would need a calculator and possibly a z-table to do get exact answers. Did he not give you any formulas for calculating these? Do you have a textbook?

 

I hope this helps a little. Good Luck

[KimboCosmo]

This is far beyond my reach...

 

 

I'd cry if I ever had to do homework like this...

[Nmj]

I Just finished something like this in school. NOT fun

[Snowhite]

oh my god!Maths again!

i wish i could help you

[LuisMa]

I also wish I could help.

 

I took a couple of statistics courses thirteen years ago, so now my brain is a bit rusted.

 

And wolfepaw, that was pretty good!!

[ZoraSourit]

I studied that at the university in 2 different classes in the 2nd and 3rd year... and that's because I was studying to become a nurse...

[wolfepaw]

Hi, celine_dion_fan. Did you take your test? How did you do?

 

I'm sorry I called you "Sofie" in my first reply to this topic. I misread who posted the topic on the topic list page. I thought it said "Soloni".

 

Well, anyway, I hope you did well.

[idroveallnight]

So I went to my teacher yesterday and all he gave me was the answers. No explenation or anything .

I have a test on tuesday and I want to know how to work the problem. Me and my group are really stressing out. We dont have

book for class only powerpoints and he hasn't even posted them yet. Im really stressing out ! I would really apreciate it any help.

 

Scores on a well known test of creativity are normally distributed in the population,

with a population mean of 450 and a population standard deviation of 96.

All scores on the test are whole numbers.

 

1. Calculate the percentile ranks for the following scores

400 -

2. Calculate the following percentiles.

45th -3. What is the probability (to four decimal places) of randomly selecting someone who scoredgreater than 516?less than 616?

 

Thanks a bunch !!!

 

Luckily I'm taking statistics this semester but I only know how to answer question three. The first thing you need to do is calculate the Z-score.

 

If the population mean is 450 and there is a standard deviation of 96:

p(X>516) -->

 

The formula for calculating a Z-score is here: http://www.measuringusability.com/images/z_pop.jpg

 

So... (516-450)/96 = 0.6875 --> This is your Z-score. It can be rounded to 0.68 or 0.69.

 

Next, you need to use a ‘unit normal’ table which is a table of Z values with the proportions (probabilities)

associated with having a score higher or lower than Z, or with having a score between the mean and z. You first locate 0.68 or 0.69 in the Z-score column. Since you are looking for scores greater than 516, you shift over to column C, which is the proportion of scores in the tail of the normal distribution curve.... and the probability is 0.2483 if you chose 0.68 as your Z-score or 0.2451 if you chose 0.69 as your Z-score.

 

To calculate the probability for 616, you use the same formula above...

 

So p(X<616) -->

 

(616-450)/96 = 1.729 or roughly 1.73 --> This again is your Z-score.

 

Again you follow the same procedure, EXCEPT this time since you are looking for the probability of scoring less than 616, you must look at column B in the unit normal table. Column B is the proportion of scores in the body of the normal distribution curve. This gives you a probability of 0.9582.

 

Here is a link that provides you with downloadable word documents of the unit normal table. It provides you with Z-score data up to Z=4.00. Regularly, Z-scores above 2.00 are considered extreme.

 

http://kate.laport.googlepages.com/unitnormaltable

 

Hope this helps

[Krys]

even since i left high school, i never want to see math again i used to remember how to do this though

[Love,]

even since i left high school, i never want to see math again i used to remember how to do this though

LOL I feel the same way...

 

But when I entered college, I had to one math class per semester for the first year, and it was my least favorite class. Just imagine this: five days a week, there is a two-hour math class, and then there's a quiz at the beginning of each class period, and there's a homework with up to 100 questions each day! I think I spent about 20 hours a week on that class alone... and I'm not talking about test weeks! :blink:

 

That's another reason why I switched to the arts!

Edited October 2, 2008 at 04:23 AM by Love,

[celine_dion_fan]

You guys are the absolute BEST.

Yeah I had the test this week, I wont find out until tuesday how I did.

This class is wearing me out.

Thanks so much for yall's help!!

[DianaLuts]

Ehh, I am going to take staticstics spring semester. Would rather take Calculus II but Stats will satisfy both Bio and Business degress since I am short on time to do them separately.